1. Field of Invention
The present invention relates to a vehicle lamp assembly, and to vehicle bulb shields, and more specifically to a vehicle bulb shield manufactured from a tailor welded steel strip of different materials to obtain desired features in each component of the vehicle bulb shield from each material within the tailor welded steel strip.
2. Background of the Related Art
A vehicle bulb shield, which is generally made from sheet metal, is mounted within a vehicle lamp assembly in front of the bulb of a vehicle headlamp to prevent emission of glare light and to generate a desirable light pattern. Due to the working environment of a vehicle, bulb shields are required to have enough vibration durability to service a committed lifecycle or service life of the vehicle. Vehicle bulb shields are required to meet specific vibration tests such as SAE J577. These vibration tests involve a multi-axis shaking of the vehicle bulb shield over a range of frequencies. The purpose of these vibration tests is to ensure the vehicle bulb shield will remain in place and intact during the service life of the vehicle. Should the vehicle bulb shield fail to maintain its position or presence as intended, the vehicle headlamp would emit a beam pattern outside of the federally mandated constraints as described in FMVSS 108. Emission of light or a beam pattern outside the required federal parameters would potentially create unsafe conditions for the driver or the driving of an oncoming vehicle, such as reduced visibility, and could potentially cause discomfort or disabling glare to oncoming drivers.
Prior art vehicle bulb shields are generally composed of two major features: one is a deep drawn shield or cup portion, which is positioned in front of the vehicle headlamp bulb, and is designed to generate a desired photometric pattern of light from the headlamp; second is a rigid leg portion which secures the bulb shield within the vehicle lamp assembly, maintains the desired bulb shield position and ensures vibration durability. Thus, a successful bulb shield design requires the sheet metal material to possess a high rigidity at the leg section and a high formability at the shield section.
The earliest vehicle bulb shields, made in the 1980's, were composed of three components: first, a stainless steel stamping welded at the seam, was attached to a second piece retainer, which was welded to a third mounting plate. In the 1990's, two-piece bulb shields were manufactured, where a leg portion and a cup portion were welded together and the exterior surface was nickel-chrome electroplated for corrosion protection and cosmetic appearance. The inner surface of the shield or cup portion is generally painted with high temperature resistant black paint to prevent unwanted reflections of light from the headlamp. More recently, one-piece vehicle bulb shields have been developed, as shown and described in U.S. Pat. No. 6,430,799. The one-piece vehicle bulb shield design is formed from one piece of uniform thickness steel.
The shield or cup section design of a bulb shield requires the sheet metal material to have a higher ductility to enable a successful drawing operation, or formation of the cup section. However, the leg section requires a higher strength for resistance to vibration failure during testing and service. Both the prior art two-piece and three-piece bulb shield designs could readily meet this requirement by the welding of a strong leg component, made from thinner and/or stronger sheet metal materials, to a light weight shield component made from thinner and more ductile sheet metal materials. As the one-piece vehicle bulb shield designs are limited to a uniform sheet metal material, prior art one-piece designs have either failed the vibration test due to choosing thinner or weaker sheet materials, such as cold rolled steel, or if successful, have become too expensive to manufacture, due to the use of expensive stainless steels which have both strength and ductility. A comparison of material cost and vibration durability of the three types of prior art vehicle bulb shields is summarized in Table 1.
TABLE 1Comparison of cost and vibration performance of bulb shields3 - piece bulb2 - piece bulb1 - piece bulbshieldshieldshieldMaterial CostHighestHighLowestVibration durabilityHighestHighLowest
Tailor welded blank (TWB) technology was initially developed in the 1940's and used to reduce overall part weight in a variety of applications including the automotive industry. One such application is described in U.S. Pat. No. 7,011,361. TWB technology involves welding sheets together which have different thicknesses prior to subjecting the sheets to further forming processes so the designer is able to “tailor” the location in the stamping to the specific material properties desired. The manufacture of continuous tailor welded strips is a newly developed technology.